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TemplateEngine.cs
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using System;
using System.Collections.Generic;
using System.IO;
using System.Text;
using System.Text.RegularExpressions;
namespace SourceGit.Models
{
public class TemplateEngine
{
private class Context(Branch branch, IReadOnlyList<Change> changes)
{
public Branch branch = branch;
public IReadOnlyList<Change> changes = changes;
}
private class Text(string text)
{
public string text = text;
}
private class Variable(string name)
{
public string name = name;
}
private class SlicedVariable(string name, int count)
{
public string name = name;
public int count = count;
}
private class RegexVariable(string name, Regex regex, string replacement)
{
public string name = name;
public Regex regex = regex;
public string replacement = replacement;
}
private const char ESCAPE = '\\';
private const char VARIABLE_ANCHOR = '$';
private const char VARIABLE_START = '{';
private const char VARIABLE_END = '}';
private const char VARIABLE_SLICE = ':';
private const char VARIABLE_REGEX = '/';
private const char NEWLINE = '\n';
private const RegexOptions REGEX_OPTIONS = RegexOptions.Singleline | RegexOptions.IgnoreCase;
public string Eval(string text, Branch branch, IReadOnlyList<Change> changes)
{
Reset();
_chars = text.ToCharArray();
Parse();
var context = new Context(branch, changes);
var sb = new StringBuilder();
sb.EnsureCapacity(text.Length);
foreach (var token in _tokens)
{
switch (token)
{
case Text text_token:
sb.Append(text_token.text);
break;
case Variable var_token:
sb.Append(EvalVariable(context, var_token));
break;
case SlicedVariable sliced_var:
sb.Append(EvalVariable(context, sliced_var));
break;
case RegexVariable regex_var:
sb.Append(EvalVariable(context, regex_var));
break;
}
}
return sb.ToString();
}
private void Reset()
{
_pos = 0;
_chars = [];
_tokens.Clear();
}
private char? Next()
{
var c = Peek();
if (c is not null)
_pos++;
return c;
}
private char? Peek()
{
return (_pos >= _chars.Length) ? null : _chars[_pos];
}
private int? Integer()
{
var start = _pos;
while (Peek() is >= '0' and <= '9')
{
_pos++;
}
if (start >= _pos)
return null;
var chars = new ReadOnlySpan<char>(_chars, start, _pos - start);
return int.Parse(chars);
}
private void Parse()
{
// text token start
var tok = _pos;
bool esc = false;
while (Next() is { } c)
{
if (esc)
{
esc = false;
continue;
}
switch (c)
{
case ESCAPE:
// allow to escape only \ and $
if (Peek() is ESCAPE or VARIABLE_ANCHOR)
{
esc = true;
FlushText(tok, _pos - 1);
tok = _pos;
}
break;
case VARIABLE_ANCHOR:
// backup the position
var bak = _pos;
var variable = TryParseVariable();
if (variable is null)
{
// no variable found, rollback
_pos = bak;
}
else
{
// variable found, flush a text token
FlushText(tok, bak - 1);
_tokens.Add(variable);
tok = _pos;
}
break;
}
}
// flush text token
FlushText(tok, _pos);
}
private void FlushText(int start, int end)
{
int len = end - start;
if (len <= 0)
return;
var text = new string(_chars, start, len);
_tokens.Add(new Text(text));
}
private object TryParseVariable()
{
if (Next() != VARIABLE_START)
return null;
var nameStart = _pos;
while (Next() is { } c)
{
// name character, continue advancing
if (IsNameChar(c))
continue;
var nameEnd = _pos - 1;
// not a name character but name is empty, cancel
if (nameStart >= nameEnd)
return null;
var name = new string(_chars, nameStart, nameEnd - nameStart);
return c switch
{
// variable
VARIABLE_END => new Variable(name),
// sliced variable
VARIABLE_SLICE => TryParseSlicedVariable(name),
// regex variable
VARIABLE_REGEX => TryParseRegexVariable(name),
_ => null,
};
}
return null;
}
private object TryParseSlicedVariable(string name)
{
int? n = Integer();
if (n is null)
return null;
if (Next() != VARIABLE_END)
return null;
return new SlicedVariable(name, (int)n);
}
private object TryParseRegexVariable(string name)
{
var regex = ParseRegex();
if (regex == null)
return null;
var replacement = ParseReplacement();
if (replacement == null)
return null;
return new RegexVariable(name, regex, replacement);
}
private Regex ParseRegex()
{
var sb = new StringBuilder();
var tok = _pos;
var esc = false;
while (Next() is { } c)
{
if (esc)
{
esc = false;
continue;
}
switch (c)
{
case ESCAPE:
// allow to escape only / as \ and { used frequently in regexes
if (Peek() == VARIABLE_REGEX)
{
esc = true;
sb.Append(_chars, tok, _pos - 1 - tok);
tok = _pos;
}
break;
case VARIABLE_REGEX:
// goto is fine
goto Loop_exit;
case NEWLINE:
// no newlines allowed
return null;
}
}
Loop_exit:
sb.Append(_chars, tok, _pos - 1 - tok);
try
{
var pattern = sb.ToString();
if (pattern.Length == 0)
return null;
var regex = new Regex(pattern, REGEX_OPTIONS);
return regex;
}
catch (RegexParseException)
{
return null;
}
}
private string ParseReplacement()
{
var sb = new StringBuilder();
var tok = _pos;
var esc = false;
while (Next() is { } c)
{
if (esc)
{
esc = false;
continue;
}
switch (c)
{
case ESCAPE:
// allow to escape only right-brace
if (Peek() == VARIABLE_END)
{
esc = true;
sb.Append(_chars, tok, _pos - 1 - tok);
tok = _pos;
}
break;
case VARIABLE_END:
// goto is fine
goto Loop_exit;
case NEWLINE:
// no newlines allowed
return null;
}
}
Loop_exit:
sb.Append(_chars, tok, _pos - 1 - tok);
var replacement = sb.ToString();
return replacement;
}
private static bool IsNameChar(char c)
{
return (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z') || (c >= '0' && c <= '9') || c == '_';
}
// (?) notice or log if variable is not found
private static string EvalVariable(Context context, string name)
{
if (!s_variables.TryGetValue(name, out var getter))
return string.Empty;
return getter(context);
}
private static string EvalVariable(Context context, Variable variable)
{
return EvalVariable(context, variable.name);
}
private static string EvalVariable(Context context, SlicedVariable variable)
{
if (!s_slicedVariables.TryGetValue(variable.name, out var getter))
return string.Empty;
return getter(context, variable.count);
}
private static string EvalVariable(Context context, RegexVariable variable)
{
var str = EvalVariable(context, variable.name);
if (string.IsNullOrEmpty(str))
return str;
return variable.regex.Replace(str, variable.replacement);
}
private int _pos = 0;
private char[] _chars = [];
private readonly List<object> _tokens = [];
private delegate string VariableGetter(Context context);
private static readonly IReadOnlyDictionary<string, VariableGetter> s_variables = new Dictionary<string, VariableGetter>() {
{"branch_name", GetBranchName},
{"files_num", GetFilesCount},
{"files", GetFiles},
{"pure_files", GetPureFiles},
};
private static string GetBranchName(Context context)
{
return context.branch.Name;
}
private static string GetFilesCount(Context context)
{
return context.changes.Count.ToString();
}
private static string GetFiles(Context context)
{
var paths = new List<string>();
foreach (var c in context.changes)
paths.Add(c.Path);
return string.Join(", ", paths);
}
private static string GetPureFiles(Context context)
{
var names = new List<string>();
foreach (var c in context.changes)
names.Add(Path.GetFileName(c.Path));
return string.Join(", ", names);
}
private delegate string VariableSliceGetter(Context context, int count);
private static readonly IReadOnlyDictionary<string, VariableSliceGetter> s_slicedVariables = new Dictionary<string, VariableSliceGetter>() {
{"files", GetFilesSliced},
{"pure_files", GetPureFilesSliced}
};
private static string GetFilesSliced(Context context, int count)
{
var sb = new StringBuilder();
var paths = new List<string>();
var max = Math.Min(count, context.changes.Count);
for (int i = 0; i < max; i++)
paths.Add(context.changes[i].Path);
sb.AppendJoin(", ", paths);
if (max < context.changes.Count)
sb.Append($" and {context.changes.Count - max} other files");
return sb.ToString();
}
private static string GetPureFilesSliced(Context context, int count)
{
var sb = new StringBuilder();
var names = new List<string>();
var max = Math.Min(count, context.changes.Count);
for (int i = 0; i < max; i++)
names.Add(Path.GetFileName(context.changes[i].Path));
sb.AppendJoin(", ", names);
if (max < context.changes.Count)
sb.Append($" and {context.changes.Count - max} other files");
return sb.ToString();
}
}
}